Tunnel excavations in deep rocks provide stress perturbations which initiate diffuse and/or localized damage propagation in the material. This damage phenomenon can lead to significant irreversible deformations and changes in rock properties. In this paper, we propose to model such behavior by considering a micromechanically-based damage approach. The resulting micromechanical model, which also accounts for initial stress, is described and assessed through the numerical analysis of a synthetic tunnel drilling in Opalinus Clay. A particular emphasis is put on the numerical integration of the model. In particular, an appropriate choice of the latter is required to ensure the numerical stability and a confident prediction of excavation damaged zone around tunnels. [less ▲]

in Fifth International Conference on Advanced COmputational Methods in ENgineering (ACOMEN 2011) (2011)

In a recent study (Levasseur et al., 2010), we proposed a class of isotropic damage models which account for initial stresses. The present paper extends this approach to anisotropic damage due to growth ... [more ▼]

In a recent study (Levasseur et al., 2010), we proposed a class of isotropic damage models which account for initial stresses. The present paper extends this approach to anisotropic damage due to growth of an arbitrarily penny-shaped microcracks system. The basic principle of the upscaling technique in the presence of initial stress is ﬁrst recalled. Then, we derive a closed-form expression of the elastic energy potential corresponding to a system of arbitrarily oriented microcracks. Thanks to the investigation of the inﬂuence of initial stresses on the material response under non monotonous loading paths, it is shown how the coupling between initial stresses and damage is strongly dependent of the microcracks density and orientation. In case of a particular distribution of microcracks orientation, described by a second order damage tensor, this model corresponds to a generalization of the macroscopic damage model of Halm and Dragon (1996), for which a physically-based interpretation can be proposed. [less ▲]

A zone with signiﬁcant irreversible deformations and signiﬁcant changes in ﬂow and transport properties is expected to be formed around underground excavation in the deep geological layers considered for ... [more ▼]

A zone with signiﬁcant irreversible deformations and signiﬁcant changes in ﬂow and transport properties is expected to be formed around underground excavation in the deep geological layers considered for the high level radioactive waste disposal. The present study concerns the modeling of this phenomena by a micromechanical damage model, based on a Mori-Tanaka homogenization on a cracked media. This anisotropic model is derived from Eshelby homogenized scheme, on which a coupling between damage and friction is taking into account on cracks. Compared to elastoplastic model on tunnel drilling modeling, micromechanical modeling seems very promising: both approaches provide similar EDZ sizes and shapes even if they do not have the same effects on perturbed mechanical behavior; micromechanical model also overcomes the elastoplastic one by a realistic characterization of crack processes. [less ▲]

in PROCEEDINGS OF THE 2nd INTERNATIONAL SYMPOSIUM ON COMPUTATIONAL GEOMECHANICS (COMGEO I ) (2011)

A zone with signiﬁcant irreversible deformations and signiﬁcant changes in ﬂow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation ... [more ▼]

A zone with signiﬁcant irreversible deformations and signiﬁcant changes in ﬂow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation around the excavation could lead to a signiﬁcant increase of the permeability, related to diffuse and/or localized crack propagation in the material. The main objective of the study is to model these processes at large scale with a micromechanical damage approach, based on the Ponte-Castaneda and Willis approximation (PCW) in the presence of initial stress, in order to assess the crack impacts on the performance of radioactive waste geological repositories. Combined with this model, permeability tensor is described as a function of micromechanical damage that is generated during the excavation. Advantages and drawbacks of this approach are described thanks to the results on Opalinus Clay and of the Selfrac long term dilatometer experiment. [less ▲]

In a recent study [15], we proposed a class of isotropic damage models which account for initial stresses. The present paper extends this approach to anisotropic damage due to growth of an arbitrarily ... [more ▼]

In a recent study [15], we proposed a class of isotropic damage models which account for initial stresses. The present paper extends this approach to anisotropic damage due to growth of an arbitrarily penny-shaped microcracks system. The basic principle of the upscaling technique in the presence of initial stress is ﬁrst recalled. Then, we derive a closed-form expression of the elastic energy potential corresponding to a system of arbitrarily oriented microcracks. It is shown that the coupling between initial stresses and damage is strongly dependent of the microcracks density and orientation. Predictions of the proposed model are illustrated through the investigation of the inﬂuence of initial stresses on the material response under non monotonous loading paths. Finally, by considering a particular distribution ofmicrocracks orientation, described by a second order damage tensor, it is shown that the model is a generalization of the macroscopic damage model of Halm and Dragon [9], for which a physically-based interpretation is then proposed. [less ▲]

The mechanical behaviors of geomaterials are significantly affected by the presence of voids or cracks-like defects. The modeling of such behavior is classically performed by considering purely ... [more ▼]

The mechanical behaviors of geomaterials are significantly affected by the presence of voids or cracks-like defects. The modeling of such behavior is classically performed by considering purely macroscopic or micromechanically-based damage models. In the perspective of applications in civil engineering or in geomechanics, we propose in this paper to evaluate a homogenization approach, based on Mori-Tanaka scheme, applied to micro-cracked materials. In order to provide an appropriate interpretation of the nonlinear behavior at macro-scale, the crack-induced damage is coupled to friction phenomena on closed cracks lips. The predictions of the coupled model are first analyzed on laboratory tests performed on Callovo-Oxfordian Clay. Then, they are extended to a numerical analysis of excavation damaged zones around tunnels [less ▲]

The mechanical behaviours of geomaterials are significantly affected by the presence of voids or cracks-like defects. The modelling of such behaviour is classically performed by considering purely ... [more ▼]

The mechanical behaviours of geomaterials are significantly affected by the presence of voids or cracks-like defects. The modelling of such behaviour is classically performed by considering purely macroscopic or micromechanically-based damage models. In the perspective of applications in civil engineering or in geomechanics, we propose in this paper to evaluate a homogenization approach, based on Mori-Tanaka scheme, applied to microcracked materials. In order to provide an appropriate interpretation of the nonlinear behaviour at macro-scale, the crack-induced damage is coupled to friction phenomena on closed cracks lips. The predictions of the coupled model are first analysed on laboratory tests performed on Callovo-Oxfordian Clay. Then, they are extended to a numerical analysis of excavation damaged zones around tunnels. [less ▲]